Quick questions on Ecological succession and keystone species: QCE Biology Unit 3

Primary succession begins on a substrate that has no existing soil or biological community. Examples of starting points: a fresh lava flow, glacial moraine, a newly formed coral cay, bare rock exposed by retreating ice.

Secondary succession occurs after a disturbance that removes the existing community but leaves the soil intact. Examples: a bushfire, a cyclone, a cleared paddock left to regenerate.

A keystone species has a disproportionately large effect on its community relative to its abundance. Three common modes of keystone action:

Top predators suppress mid-level consumers. Example: the dingo (Canis dingo) in arid Australia. Dingoes suppress red fox and feral cat populations, indirectly protecting small mammal diversity.

A species that physically modifies the environment. Example: the bilby (Macrotis lagotis) and other digging marsupials turn over large volumes of soil each year, mixing organic matter, capturing leaf litter and creating microhabitats. Their loss across most of mainland Australia has reduced soil function in arid ecosystems.

A species whose mutualistic role supports many others. Example: flying foxes (Pteropus species) pollinate and disperse seeds for dozens of eucalypt and rainforest tree species along the east coast. Their decline reduces seed dispersal distance and forest regeneration.

Distinguish between primary and secondary succession and give one Australian example of each. [3 marks]

A graph shows species richness rising from 0 to 60 over 50 years post-disturbance, with rapid early gains levelling near year 30. Identify which phase reflects pioneer arrival and which reflects climax community, and explain the levelling. [3 marks]

Refer to a keystone species. (a) Define keystone species. (b) Identify the role of cassowaries in Daintree succession.